Failing to write xml document

I have created a class for building and saving an xml document to file but I can not work out why the contents of the xml is empty, and why I have to save the file in the parent directory.

I am creating a Jsp/Servlet Java webservice.

The class is supposed to get a list of testimonials from a MySQL database and generate a new XML document containing the testimonial data.

I am calling the class and methods in the doPost() method of a servlet. When a user clicks a button in on a web page the xml document is generated/updated.

Here is the class:

public class XMLGenerator {

    private String xmlString;
    private List<Testimonial> list;
    private TestimonialService ts;
    private Document xmlDoc;

    public XMLGenerator(TestimonialService ts){
        this.ts = ts;
        list = new ArrayList<>();
        xmlDoc = updateXmlDocument();

    }

    // generate xml string
    private void updateXmlString(){

        xmlString = "<?xml version=\\\"1.0\\\" encoding=\\\"UTF-8\\\" standalone=\\\"yes\\\"?>";

        list.clear();
        list = updateTestimonialList();

        for(Testimonial test : list){
            xmlString += "<testimonial>";
            xmlString += "<id>" + test.getID() + "</id>";
            xmlString += "<content>" + test.getTestimonial() + "</content>";
            xmlString += "<author>" + test.getAuthor() + "</author>";
            xmlString += "<date>" + test.getDate() + "</date>";
            xmlString += "</testimonial>";
        }
    }

    // get list of testimonials
    public List<Testimonial> updateTestimonialList(){
        list.clear();
        try {
            list = ts.getTestimonials();
        }catch(SQLException e){
            e.printStackTrace();
        }
        return list;
    }

    // add testimonials to xml document
    public Document updateXmlDocument() {

        updateXmlString();

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder;
        try
        {
            builder = factory.newDocumentBuilder();
            xmlDoc = builder.parse( new InputSource( new StringReader( xmlString ) ) );
            return xmlDoc;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    // write xml file
    public boolean writeXmlToFile(){
        boolean success = false;
        try {
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();

            DOMSource source = new DOMSource(xmlDoc);
            StreamResult result = new StreamResult(new File("../testimonials.xml"));

            transformer.transform(source, result);
            success = true;
        }catch(TransformerException tr){
            tr.printStackTrace();
        }
        return success;
    }
}

Two questions:

1) Why is the xmlString converting to an empty XmlDocument?

2) Why do I have to save the xml file to the parent directory and not the WEB-INF folder?